Re: Thin device provisioning

[Jamie Lokier <jamie@shareable.org>]

Matthew Wilcox wrote:
> I've spoken with a few Linux filesystem people.  They find it
> significantly easier to send a single LBA/length pair at a time.
> Modern filesystems try quite hard to keep fragmentation to a minimum, so
> they don't expect a performance hit from sending multiple commands.
> They're non-blocking writes, and the IO elevators can take care of
> sending more important reads first.

Perhaps there are occasions when it's more efficient for the disk to
process several LBA/length pairs in a single operation?

I.e. you send the first pair, the disk starts working, then you send
the second, and that's not as efficient as doing both at the same
time, which might translate to a single commit on SSD.

The general solution to that would be a 'CORK' operation, though,
similar to TCP_CORK: this operation will be followed by others, you
may start it now, but don't rush...

-- Jamie